Mechanical properties and water vapour permeability of hydrolysed collagen–cocoa butter edible films plasticised with sucrose

The aim of this study was to develop and characterise edible films produced from hydrolysed collagen and cocoa butter and plasticised with sucrose. The mechanical properties, water vapour permeability, opacity and morphology of the films were characterised. The film composition that yielded the best results was used to produce a coating for application in chocolate panned products. A water-based coating with desirable barrier properties that could replace shellac is important for the environment as well as health, and also because chocolate products have great appeal among children. The films obtained were easily manageable and flexible. Sucrose reduced tensile strength (TS), while hydrolysed collagen at concentrations above 15% increased it. Cocoa butter resulted in less-resistant films. The elongation at break values (EAB%) were higher for films containing higher sucrose concentrations. The water vapour permeability (WVP) ranged from 0.32 to 0.63 g mm m⁻² h⁻¹ kPa⁻¹. For the same concentration of cocoa butter, the WVP was directly affected by the thickness of the film, i.e., the greater the thickness, the higher the WVP. Cocoa butter increased film opacity, while sucrose decreased it, particularly at concentrations above 17.5%. High concentrations of hydrolysed collagen produced films with more homogeneous surfaces. The brightness of the product with the coating developed in this study was attractive; however the brightness of the product with shellac was considered more intense. The properties of these films indicate that they are promising systems for coating chocolate panned products.     

Properties of triticale flour protein based films

Triticale flour proteins based films were developed. Solubility in water, water vapor permeability (WVP), and mechanical properties of triticale films are presented. The effects of thermal treatments and glycerol concentration were also evaluated. WVP values were in the range 0.10-4.22 × 10⁻¹⁰ g m⁻¹ s⁻¹ Pa⁻¹. Tensile strength (TS) and percentage of elongation (%E) were in the range 2.9-0.20 MPa and 250-110% respectively. Total soluble matter (TSM), WVP, and %E decreased with the increase in the curing temperature. More plasticized films presented greater TSM, WVP, %E and lower values of TS. At a giving temperature (T) and glycerol concentration, an increase in relative humidity (RH) resulted in higher values of TSM, WVP, %E and lower TS values. It was observed that in films with the same treatments and conditioning, WVP increased with the increase in measurement temperature. Triticale proteins showed suitable film-forming capacity for the formulation of biodegradable films.     

Effect of some factors and pretreatment on the properties of porcine plasma protein-based films

The properties of porcine plasma protein-based films as influenced by some factors and pretreatment were studied. Both protein concentrations (20 and 30 g L⁻¹) and glycerol contents (50, 60 and 70 g/100 g protein) had the impact on film properties. Film prepared from film-forming solution (FFS) containing protein (30 g L⁻¹) and glycerol (60 g/100 g protein) possessed the highest tensile strength (TS) (2.48 MPa), while that containing protein (30 g L⁻¹) and glycerol (70 g/100 g protein) exhibited the greatest elongation at break (EAB) (18.33%). Protein and glycerol contents affected water vapor permeability (WVP) and transparency of the resulting films. No differences in protein solubility were found among all films (p > 0.05). Pretreatment of FFS by adjusting pH (2-11) and heating at different temperatures (40, 55 and 70 °C) on the properties of the resulting films was investigated. TS and EAB became higher but WVP decreased with decreasing or increasing pH value of FFS. Heat treatment of FFS with pH 3 and 10 had no impact on TS of the resulting film (p > 0.05). On the other hand, EAB and WVP increased with increasing temperature of FFS at both pHs (p < 0.05).     

Effects of plasticizers, pH and heating of film-forming solution on the properties of pea protein isolate films

Effects of glycerol (3-7% w/w) and sorbitol (4-8% w/w) concentration, pH (7.0, 9.0, 11.0) and heating (90 °C, 20 min) of film-forming solution (FFS) on the water vapor permeability (WVP), moisture content (MC), solubility, light transmission and transparency of pea protein isolate (PPI) films were investigated. Films plasticized with sorbitol exhibited significantly lower WVP, lower MC and higher solubility, in comparison with glycerol-plasticized films. Increasing glycerol content of the films led to increases in WVP and MC but did not affect film solubility. In contrast, increase in sorbitol content had no effect on permeability and MC but resulted in increased film solubility. Moisture sorption isotherms of PPI films suggested that the difference in WVP observed among films plasticized with glycerol and sorbitol might be due to the different hygroscopicity of these plasticizers. The pH of FFS did not have a significant effect on WVP and MC. Solubility of PPI films formed from non-heated FFS was not affected by pH, whereas solubility of films formed from heat-treated FFS generally increased when pH was increased from 7.0 to 11.0. Heating of FFS resulted in improved film transparency. All tested films were characterized by excellent ability to absorb UV radiation. Microstructural observation by scanning electron microscopy did not show differences between sorbitol- and glycerol-plasticized films.     

Relationship between protein characteristics and film‐forming properties of kidney bean,field pea and amaranth protein isolates

This study was undertaken to evaluate physicochemical (colour, protein content, ash content and zeta potential), structural (size exclusion chromatography and thermal properties) and film‐forming properties of kidney bean, field pea and amaranth protein isolates (KBPI, FPPI and AMPI, respectively). Protein content, ash content, zeta potential and denaturation temperature of the isolates ranged from 83.9 to 91.4%, 2.9 to 4.5%, ?37.3 to ?44.2 mV and 85.5 to 96.2 °C, respectively. Size exclusion chromatography revealed that globulins were prominent proteins in KBPI and FPPI, while AMPI contained both globulins and albumins as major fractions. FPPI showed the highest L* value (88.1), surface charge (zeta potential = –44.2 mV) and protein solubility (80.0–94.2%). Films were prepared from heated (90 °C for 20 min) and unheated protein dispersions of pH 7.0, 8.0 and 9.0 and evaluated for colour, opacity, tensile strength (TS), water‐solubilised matter (WSM) and water vapour permeability (WVP). FPPI films showed the most desirable properties in terms of the highest L* (87.5–90.5), TS (12.6–37.2 MPa) and the lowest opacity (7.1–8.4 A₆₀₀/mm). FT‐IR spectroscopic analysis of the films revealed that alkaline pH and heat treatment unfolded protein molecules. Alkaline pH reduced opacity, while heat treatment improved TS and water resistance (decreased WSM and WVP) of protein films, which varied with the protein isolates.     

Effects of plasticizers and nano-clay content on the physical properties of chicken feather protein composite films

To prepare chicken feather protein (CFP)/nano-clay composite films and to evaluate the effects of various plasticizers and nano-clay concentrations on the mechanical properties of the films, CFP composite films with various concentrations of Cloisite Na⁺ were prepared, and their physical properties such as tensile strength (TS), elongation at break (E), and water vapor permeability (WVP) were investigated. Optimal CFP films were formed with 5 g of CFP, 0.5 g of glycerol, and 1.5 g of sorbitol in 100 mL of film-forming solution; the TS, E, and WVP of the film were 4.74 MPa, 10.08%, and 3.11 × 10⁻⁹ g m/m² s Pa, respectively. After the nano-clay was incorporated into the CFP film-forming solution, scanning electron microscopy and X-ray diffraction studies were conducted to examine the structural characteristics of the CFP/nano-clay composite films. The incorporation of nano-clay improved the physical properties of the CFP films. The TS of the CFP/nano-clay composite film containing 7% Cloisite Na⁺ increased by 1.21 MPa, and the WVP of the composite film decreased by 1.15 × 10⁻⁹ g m/m² s Pa compared to the CFP film. Therefore, these results suggest that CFP composite films can be prepared with improved mechanical property by the addition of nano-clay and used as a food packaging material in the food industry.     

Structure-modifying alkaline and acidic pH-shifting processes promote film formation of soy proteins

The effect of pH-shifting, a process that induces the molten globule state in proteins, on the film-forming potential of soy protein isolate (SPI) at different temperatures was investigated. Partial unfolding at pH 1.5 or 12, followed by refolding at pH 7.0, was performed to alter the protein structure. Glycerin-plasticised films were prepared from pH-treated SPI at ambient temperature (20 °C), or by heating at 50, 60, 70, or 80 °C (30 min). Tensile strength (TS), elongation at break (EAB), water vapour permeability (WVP), protein solubility (pH 3–7), and non-participating proteins of films were analysed, and the film microstructures were examined. The pH₁₂-treated SPI spontaneously formed a transparent, slightly yellowish film at 20 °C, which had the greatest EAB, while pH_1.5-treated and native SPIs required preheating at 50 and 70 °C, respectively, to form a film. Heating generally decreased solubility and WVP but increased TS. Films formed from both pH₁₂- and pH_1.5-treated SPIs were more elastic (up to 2-fold greater in EAB, P < 0.05) than the film formed from untreated SPI despite slightly reduced TS and WVP. Electrophoresis revealed disulphide bonds between A and B subunits of glycinin being a dominant force in pH₁₂- and pH_1.5-treated SPI films, while noncovalent forces were abundant in untreated SPI films. The pH₁₂-treated SPI film consisted of more interactive protein strands than other SPI films, which seemed to explain its superior elastic properties.     

Effects of glycerol,sorbitol, xylitol and fructose plasticisers on mechanical and moisture barrier properties of pullulan–alginate–carboxymethylcellulose blend films

The effects of glycerol, sorbitol, xylitol and fructose plasticisers on water sorption, mechanical properties, water vapour permeability (WVP) and microstructure of pullulan–alginate–carboxymethycellulose (PAC) blend films were investigated. At low plasticiser concentrations (below 7% w/w dry basis), antiplasticisation effect was observed, causing an increase in tensile strength (TS) but a decrease in the equilibrium moisture content. As glycerol concentration increased from 0% to 7%, TS increased from 68.1 to 69.6 MPa, whereas equilibrium moisture contents at 0.84 a_w decreased from 0.37 to 0.3 g H₂O g^?1 dry basis. At higher plasticiser concentrations (14–25% w/w), an opposite trend was observed on the PAC films, resulting in the reduction of TS and elevation of moisture content. Among the four plasticisers tested, the fructose‐plasticised films were the most brittle, showing the highest TS, but had the lowest elongation at break (EAB), WVP and equilibrium moisture content values than films plasticised with other polyols. On the other hand, glycerol resulted in the most flexible film structure, exhibiting opposite materials' properties as compared with the fructose‐plasticised films. For instance, at 25% (w/w) plasticiser concentration, EAB and WVP values of fructose‐plasticised films were 33.5% and 3.48 × 10^?6 g m Pa^?1 h^?1 m^?2, which were significantly lower than that of glycerol‐plasticised films (58.6% and 4.86 × 10^?6 g m Pa^?1 h^?1 m^?2, respectively). Scanning electron microscopy showed that the plasticised PCA films were less homogeneous and more porous than the unplasticised counterparts, indicating that plasticisers had an effect on the microstructural morphology of the film matrix.     

Preparation and characterization of proteinous film from lentil (Lens culinaris): Edible film from lentil (Lens culinaris)

This study was conducted to extract protein from lentil seed and prepare edible film from the protein and to determine mechanical, optical and barrier properties of lentil protein concentrate (LPC) film. The film was prepared from LPC (5 g/100 ml water) and glycerine (50%, w/w of LPC). Hunter color value (L, a and b), tensile strength, percentage elongation at break (E), puncture strength, water vapor permeability (WVP), moisture content after conditioning at 50% RH and 25 °C for 48 h and total soluble matter after immersion in water, were measured. In regarding to WVP, in spite of difference in film thickness and relative humidity of experiment in different studies, lentil protein film is comparable with other protein films. Characteristics of the lentil protein-based edible films were comparable with other edible protein films. LPC film had more red and less yellow color; it seems that the film had good mechanical properties and water vapor permeability in concomitant with good solubility.     

Physico-chemical properties,morphology and antioxidant activity of film from fish skin gelatin incorporated with root essential oils

The influences of three root essential oils (ginger, turmeric and plai) at different levels (25%, 50% and 100%, based on protein content) on properties and antioxidative activity of fish skin gelatin-based film were investigated. Films incorporated with all essential oils showed the lower tensile strength (TS) but higher elongation at break (EAB) with increasing amount of essential oils, compared with the control film (without oil incorporated), regardless of types of essential oil (p < 0.05). Water vapor permeability (WVP) of films containing essential oils decreased as the amount of essential oils increased (p < 0.05). Decreases in L^*-value and increases in b^*-, ΔE^*- and transparency value were observed with increasing amount of essential oils incorporated (p < 0.05). FTIR spectra indicated that films added with essential oils, especially from plai root, exhibited higher hydrophobicity than the control film, as evidenced by higher amplitude at wavenunber of 2877–2922 cm⁻¹ and 1732 cm⁻¹. Lower degradation temperature was obtained in films containing essential oils. Microstructural study revealed that bilayer films could be formed when essential oils at level above 50% were incorporated. Film incorporated with plai and turmeric essential oils showed the higher DPPH and ABTS radical scavenging activity, respectively, (p < 0.05), compared with the control film and ginger essential oil added film. Thus, the incorporation of root essential oils directly affected properties of fish skin gelatin-based film, depending on types and levels incorporated.     

Effect of plasticizer content on the functional properties of extruded gelatin-based composite films

Beef gelatin, in combination with varying levels of glycerol, was used to manufacture films by extrusion. A twin-screw co-rotating extruder was employed to produce the films and the mechanical and barrier properties of the films were investigated. Increasing the plasticizer content increased (P < 0.05) elongation at break (EAB) values but decreased (P < 0.05) tensile strength (TS) values. Oxygen permeability (OP) values for gelatin-based composite films increased (P < 0.05) as the concentration of glycerol increased. Additionally, the solubility of films in water and seal strength increased as glycerol content increased. FTIR results indicated that increasing glycerol concentration increased and displaced the peak situated around 1032 cm⁻¹, which corresponded to glycerol. Gelatin-based composite films with a concentration of 0.2% glycerol possessed the lowest water vapor permeability (WVP) and OP values. From the data generated in this study, it is clear that the use of a plasticizing agent in film formulations should be carefully considered because of the negative effects that the plasticizing agent could have on extruded film barrier properties.     

Effect of select parameters on the properties of edible film from water-soluble fish proteins in surimi wash-water

Edible film from water-soluble fish proteins were developed by casting film solution on leveled trays and effects of pH (9.5, 10.0 and 10.5), heating temperature (60, 70 and 80 °C), and heating time (10, 20 and 30 min) of the film solution on various film properties were determined using Response Surface Methodology (RSM). The impact of pH and heating temperature of film solution was more significant, overall, on the film's properties than heating time. Contour plots of tensile strength and elongation at break was highest at pH of 10.0 at 70 °C (2.75-3.02 MPa) but low in elongation at break (6.35-9.16%), while water vapor permeability and oxygen permeability were at their lowest (58.55-65.96 g mm/m² d kPa and 351.33-624.18 cm³ μm/m² d kPa). There was a direct correlation between the films’ and proteins’ solubility on one hand, and heating temperature of film solution on the other, which reversed with change in pH of film solution. Film color was darker and more yellowish with increase in the pH of film solution.     

Effects of pH and Salts on Physical and Mechanical Properties of Pea Starch Films

To identify the significant contribution of intermolecular hydrogen bonds of starch molecules to the film structure formation, pH of film‐forming solutions was adjusted and also various salts (NaCl, CaCl₂, CaSO₄, and K₂SO₄) were mixed into the glycerol‐plasticized pea starch film. The film made from pH 7 possessed the highest tensile strength‐at‐break (2 times) and elastic modulus (4 to 15 times) and the lowest elongation‐at‐break compared with those of the films made from acid and alkali environments. The pH 7 film also has the highest film density and the lowest total soluble matter. At the level of 0.01 to 0.1 M of CaSO₄ and 0.1 M of K₂SO₄ in a kilogram of starch, the water solubility of the film increased, while chloride salts slightly lowered the solubility. NaCl and CaSO₄ reduced water vapor permeability (WVP), while CaCl₂ slightly increased WVP at 0.01 and 0.06 M concentrations, and K₂SO₄ significantly increased WVP at 0.03 and 0.15 M. Presence of salts increased tensile strength (5 to 14 times than the control films) and elastic modulus (35 to 180 times) of starch film at 0.01 to 0.03 M of CaSO₄ and K₂SO₄. Elongation‐at‐break increased significantly as salt concentration increases to an optimal level. However, when the concentration exceeded above the optimal level, the E of starch films decreased and showed no significant difference from the control film. Overall, the addition of salts modified physical and mechanical properties of pea starch films more than pH adjustment without any salt addition.     

Development and characterization of a novel biodegradable edible film obtained from psyllium seed (Plantago ovata Forsk)

In this study, the physical, thermal and mechanical properties of a novel edible film based on psyllium hydrocolloid (PH) were investigated. PH films were prepared by incorporation of three levels of glycerol (15%, 25%, and 35% w/w). As glycerol concentration increased, water vapor permeability (WVP), percent of elongation (E%) and water solubility of PH films increased whilst, tensile strength (TS), surface hydrophobicity and glass transition point (T_g) decreased significantly. At the level of 15% (W/W) of glycerol, PH films showed the lowest WVP values (1.16 × 10⁻¹⁰ g H₂O m⁻² s⁻¹ MPa⁻¹), E% (24.57%) and water solubility (47.69%) and the highest values for TS (14.31 MPa), water contact angle (84.47°) and T_g (175.2 °C). By increasing glycerol concentration, PH films became slightly greenish and yellowish in color but still transparent in appearance. This study revealed that the psyllium hydrocolloid had a good potential to be used in producing edible films with interesting specifications.     

Development and characterization of cassava starch and soy protein concentrate based edible films

The sensory attributes, mechanical, water vapour permeability (WVP) and solubility properties of cassava starch and soy protein concentrate (SPC)‐based edible films of varying levels of glycerol were studied. Addition of SPC and glycerol up to 30% and 20%, respectively, reduced stickiness and improved colour and appearance of the films. Tensile strength (TS), elastic modulus (EM) and elongation at break (EAB) of films increased, while film solubility (FS) and WVP decreased with SPC and glycerol up to 50% and 20% level, respectively, ranging from 20.33 to 26.94 MPa (TS), 41.33 to 72.76 MPa (EM), 7.90 to 12.28 MPa (EAB), 15.07 to 31.90% (FS) and 2.62 to 4.13 g H₂O mm m^?2 day kPa (WVP). The TS, EAB and WVP were higher for the biofilms than for low‐density polyethylene and cellophane films.     

Water barrier and physical properties of starch/decolorized hsian-tsao leaf gum films: Impact of surfactant lamination

The moisture barrier and physical properties of bilayer films prepared by lamination of starch/decolorized hsian-tsao leaf gum (dHG) and surfactant layers were investigated. It was found that the water vapor permeability (WVP) of tapioca starch/dHG film (1.31 × 10^?10 g/m s Pa) pronouncedly decreased by the aid of a surfactant layer lamination (1.36–5.25 × 10^?12 g/m s Pa). The WVP of bilayer film increased with increasing the concentration of starch/dHG in the surfactant layer, but was not significantly influenced when it was thickened. The sorption isotherms of both monolayer and bilayer films made from starch/dHG showed typical behavior of water-vapor-sensitive hydrophilic biopolymers. However, the equilibrium moisture content of the monolayer film was significantly higher than that of bilayer films when water activity (a_w) reaches 0.33. Both the tensile and puncture force of starch/dHG films did not vary significantly by laminating a surfactant layer, indicating the mechanical strength of surfactant layer is relatively weak, and this surfactant layer mainly served as a barrier for moisture. When compared to emulsion-based starch/dHG films with surfactant, the surfactant laminated starch/dHG films showed higher water barrier property, mechanical strength, and transparency.     

Effect of PLA lamination on performance characteristics of agar/κ-carrageenan/clay bio-nanocomposite film

Multilayer films composed of PLA and agar/κ-carrageenan/clay (Cloisite® Na⁺) nanocomposite films were prepared, and the effect of lamination of PLA layers on the performance properties such as optical, mechanical, gas barrier, water resistance, and thermal stability properties was determined. The tensile strength (TS) of the agar/κ-carrageenan/clay nanocomposite films (67.8 ± 2.1 MPa) was greater than that of PLA films (43.3 ± 3.6 MPa), and the water vapor permeability (WVP), water uptake ratio (WUR), and water solubility (WS) of the nanocomposite films were higher than those of PLA films. The film properties of the multilayer films exhibited better properties of the component film layers. Especially, the WVP and water resistance of the bionanocomposite film were improved significantly, while the OTR of the PLA film decreased profoundly after lamination with PLA layers. Thermal stability of the bionanocomposite also increased after lamination with PLA layers.     

Preparation and properties of rice starch–chitosan blend biodegradable film

Biodegradable blend films from rice starch–chitosan were developed by casting film-solution on leveled trays. The influence of the ratio of starch and chitosan (2:1, 1.5:1, 1:1, and 0.5:1) on the mechanical properties, water barrier properties, and miscibility of biodegradable blend films was investigated. The biodegradable blend film from rice starch–chitosan showed an increase in tensile strength (TS), water vapor permeability (WVP), lighter color and yellowness and a decreasing elongation at the break (E), and film solubility (FS) after incorporation of chitosan. The introduction of chitosan increased the crystalline peak structure of starch film; however, too high chitosan concentration yielded phase separation between starch and chitosan. The amino group band of the chitosan molecule in the FTIR spectrum shifted from 1541.15 cm⁻¹ in the chitosan film to 1621.96 cm⁻¹ in the biodegradable blend films. These results pointed out that there was a molecular miscibility between these two components. The properties of rice starch–chitosan biodegradable blend film and selected biopolymer and synthetic polymer films were compared; the results demonstrated that rice starch–chitosan biodegradable blend film had mechanical properties similar to the other chitosan films. However, the water vapor permeability of rice starch–chitosan biodegradable blend film was characterized by relatively lower water vapor permeability than chitosan films but higher than polyolefin.     

Effects of nanoclay type on the physical and antimicrobial properties of PVOH-based nanocomposite films

Polyvinyl alcohols-based nanocomposite films with four types of montmorillonite (MMT) nanoclay, including 18-amino stearic acid (I.24TL), methyl, bis hydroxyethyl, octadecyl ammonium (I.34TCN), di-methyl, di-hydrogenated tallow ammonium/siloxane (I.44PSS) organically modified MMT and a natural MMT (Na⁺-MMT) were fabricated by a solution-intercalation, film-casting method, and effects of the nanoclays were evaluated on physical properties, including transmittance, tensile strength (TS), elongation at break (E), water solubility (WS), swelling ratio (SR), water vapor uptake ratio (WVUR), and water vapor permeability (WVP), as well as antimicrobial activity of the polyvinyl alcohols-based films. Transmittance, WS, SR, WVUR, WVP of the nanocomposite films were significantly reduced by nano-composition compared to a pure polyvinyl alcohols film. The WVP decreased by 11.8–20.7%, and WS, SR and WVUR decreased by 19.9–41.8%, 9.1–26.4%, and 4.8–12.8%, respectively. The extent of changes was dependent on nanoclay type. X-ray diffraction patterns revealed that intercalation was formed in nanocomposite films. Overall among all the tested nanoclays, Na⁺-MMT showed more impact on physical properties of polyvinyl alcohols films, and the polyvinyl alcohols film compounded with quaternary ammonium group displayed remarkable antimicrobial activity against Gram-positive bacteria.     

Development and characterization of an edible chitosan–whey protein nano composite film for chestnut (Castanea mollissima Bl.) preservation

Chitosan (CHI) and whey protein are usually used to prepare edible films for food preservation. However, the composite film composed of the two components does not yield satisfactory properties for chestnut preservation. In this study, nano-cellulose and cinnamaldehyde (CMA) were added to CHI and whey protein, creating a new composite film with strong water retention, bacteriostatic, and mechanical properties. The water vapor permeability (WVP) of the film decreased by 21.61% with the addition of 0.5% (w/v) nano-cellulose, and 23.02% with the addition of 0.3% (w/v) CMA. Furthermore, water solubility (WS) decreased 22.05%, and the density of the film was significantly improved with the addition of 0.3% (w/v) CMA. The optimized formula of the film was CHI 2.5% (w/v), whey protein 3.0% (w/v), nano-cellulose 0.5% (w/v), CMA 0.3% (w/v), and pH 3.8, as determined by orthogonal testing L9(3⁴), with fuzzy comprehensive assessment, of WVP, WS, tensile strength, and elongation at break. The film clearly inhibited the growth of E. coli, S. aureus, and Chinese chestnut fungus, destroying the mycelial structure of the fungus. In addition, coating effectively reduced the weight loss, mildew rate, and calcification index during 16 days of storage of chestnuts at 25 °C.